package march.test_3_7;

import java.util.Scanner;

public class TestMain2 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        int[] hash = new int[500];
        for(int i = 0; i < str.length(); i++) {
            hash[str.charAt(i)]++;
        }
        for (int i = 0; i < str.length(); i++) {
            if(hash[str.charAt(i)] == 1) {
                System.out.println(str.charAt(i));
                return;
            }
        }
    }
}
